This invention relates to a golf ball comprising a core and a cover of at least two inner and outer layers and more particularly, to a golf ball of such structure having an improved overall profile of performance including feel, durability, rebound, approach control and flight characteristics.
Many golf balls having different multilayer structures are known, for example, from JP-A 7-24084, 7-24085, 9-239067, and 9-239068. By tailoring their structure, these balls are improved in feel, durability and rebound.
JP-A 10-248955 discloses a two-piece solid golf ball comprising a solid core and a cover which is formed with a plurality of dimples in its surface. The plurality of dimples include at least three types of dimples which are different in diameter. The diameter (mm) divided by the depth (mm) of each dimple ranges from 18 to 27. The volume of each dimple divided by the volume of a cylinder whose diameter and height are equal to the diameter and depth of the dimple ranges from 0.390 to 0.550.
JP-A 10-151225 discloses a three-piece solid golf ball in which improvements in spin performance, feel and control with any type of club are attained by paying attention to the relationship of inertia moment to the ball structure and dimples. The ball has a high inertia moment, and the diameter/depth ratio of dimples is as low as about 17/1.
Since these proposals intend to improve the feel, durability and rebound of balls primarily by tailoring the ball structure, they fail to take full advantage of the spin performance and dimple aerodynamics having a significant influence on the flight following shots. There is thus room for further improvement.
The prior art golf balls do not fully meet the demand of users that the balls satisfy the feel, rebound, durability and approach control requirements imposed on the ball structure and offer good flight performance following shots, and thus have an advanced overall profile of performance.
An object of the invention is to provide an improved golf ball having an advanced overall profile of performance including a good feel, durability, rebound, approach control, and flight performance.
The invention is directed to a golf ball comprising a core and a cover of at least two layers around the core, the cover layers including the outermost layer which is formed with a plurality of dimples. It is understood that where the cover consists of two inner and outer layers, the outermost layer is simply referred to as the outer layer.
In the case of a golf ball having a cover consisting of two inner and outer layers, for example, it has been found that (1) spin is correlated to the hardnesses of the cover inner and outer layers such that the ball receives more spin when the cover inner or outer layer is soft, and the ball is less susceptible to spin when both the cover inner and outer layers are hard; and that (2) an optimum combination of the product of the Shore D hardness of the cover inner layer multiplied by the Shore D hardness of the cover outer layer with the overall dimple volume largely contributes to spin.
The invention provides a golf ball comprising a core and a cover of at least two layers around the core, the cover layers including the outermost layer which is formed in its outer surface with a plurality of dimples. The cover outermost layer has a Shore D hardness of 30 to less than 51. The product (Axc3x97B) of the Shore D hardness, represented by B, of the cover outermost layer multiplied by the Shore D hardness, represented by A, of a cover layer disposed inside and contiguous to the cover outermost layer is in the range of 1,000 to 3,500. It is understood that in the case of a cover consisting of inner and outer layers, the inside layer is the inner layer and in the case of a cover consisting of innermost, inner and outer layers, the inside layer is the inner layer. The plurality of dimples include at least three types of dimples which are different in diameter and have an average diameter (AD) and an average depth (AP) wherein the ratio (AD/AP) of the average diameter to the average depth is from 17/1 to 26/1. The overall dimple volume (Vs) which is the sum of the volumes of all dimple spaces each defined below a plane circumscribed by a dimple edge is in the range of 280 to 390 mm3. Preferably the cover layer hardness product (Axc3x97B) and the overall dimple volume (Vs) are correlated such that Vs becomes smaller when Axc3x97B has a large value, and vice versa. More specifically, Vs is 310 to 390 mm3 when Axc3x97B is from 1,000 to 2,500, and Vs is 280 to 340 mm3 when Axc3x97B is from 2,000 to 3,500. Owing to the proper selection of hardness for the cover inner and outer layers and the optimum combination of the hardness product with a specific overall dimple volume, both factors providing significant contributions to spin, the ball upon full shots with a driver exhibits a gradually rising, boring trajectory, improved flight characteristics, and thus an increased distance. The ball satisfies the feel, durability, rebound (or restitution) and approach control requirements imposed on the ball structure and thus has an advanced overall profile of performance over the prior art.
In preferred embodiments, the core is formed of a rubber composition based on cis-1,4-polybutadiene; and the total number of dimples is 370 to 450.